Not all children with minimal brain dysfunction (MBD) benefit from psychostimulants, and some good responders require but low dosage levels while some need high levels. This investigation aims at a priori identification of good responders as well as advance determination of optimal dosage level. The study is a double-blind, cross-over design of 6 weeks duration. Each MBD child undergoes three evaluation (baseline, on-drug, and on-placebo). Drug dosage is clinically adjusted twice weekly by a child psychiatrist. Eighty clinical subjects will participate, all Caucasian boys, aged 7 to 10, of normal intelligence. Ten normal subjects will be studied in the baseline condition. Teacher and parent ratings and tests of cognitive style are employed at each evaluation, as is the laboratory experiment. The laboratory run has two phases: a) a control study of on and off-key reaction time to 120 tones (4 intensity levels from very soft to very loud; b) a repetition of the tones comparing two conditions of reward and frustration. Heart rate, skin resistance, and brain waves are continuously recorded during the reaction time tasks. The research is modeled after Russian experiments in which reaction time to tones of increasing intensity identified subjects with strong and weak nervous systems who had different responses to caffeine.